In an image scanning device used in an image forming apparatus such as a copier, a printer or the like, the improvement of productivity of image reading is requested. Hitherto, there is a device in which a plurality of document read conveyance paths are formed, a reading sensor to read a front side image of a document and a reading sensor to read a back side image are disposed on each of the conveyance paths, and the read speed at the time of both-side reading of the document image is increased. As this image scanning device, for example, JP-A-2006-168972 discloses a device having a first branch path for conveying a document to a first read position and a second branch path for conveying a document to a second read position. Besides, for example, JP-A-2004-15299 discloses a device in which a scanner device and a CIP (Contact Image Sensor) are provided at both sides of a first conveyance path, and the scanner device and the CIS are simultaneously used to read both surfaces of a document conveyed on the first conveyance path.
However, both the devices do not increase the read speed to improve the productivity of reading when documents are continuously read.
The development of an auto document feeding device is desired in which when documents are continuously read, the arrival timing of a document at an image read position is advanced to efficiently read the document, and the productivity of reading is improved by the enhancement of the read speed of an image.